Method and apparatus for breaking up rocks containing liquid or gaseous hydrocarbons by means of explosives

ABSTRACT

Oblique holes are drilled into a formation from a well bore hole, packed with explosive charges, and simultaneously detonated. The holes are drilled at the same level and angle with respect to the bore hole, and are evenly spaced around its periphery. An implementing apparatus includes a tool carrier that is lowered into the bore hole and anchored in place, a flexible shaft drilling tool that is lowered into the carrier, and a packing tool for placing the charges.

Unite States Patent 1191 Azalbert et al.

[ METHOD AND APPARATUS FOR BREAKING UP ROCKS CONTAINING LIQUID OR GASEOUS HYDROCARBONS BY MEANS OF EXPLOSIVES' [75] Inventors: Jean Paul Azalbert,

Ablon-sur-Seine; Adrien Giraud, Paris, both of France [73] Assignee: Compagnie Francaise des Petroles,

Paris. France [22] Filed: May 21, 1971 [21] Appl. No.: 145,666

[52] US. Cl 166/299, 166/63, 166/169,,

175/4.5l, 175/61, 175/75, 175/78 [51] Int. Cl E21b 43/00 [58] Field of Search 166/63, 162, 169, 247,

[56] References Cited UNITED STATES PATENTS 3.002.454 10/1961 Chesnut 166/299 Mar. 19, I974 2,500,785 3/1950 Arutunoff 175/78 2.839.270 6/1958 McCune et al. 175/61 9/1964 Garrison 175/78 Primary Examiner-Ernest R. Purser Assistant Examiner-Jack E. Ebel Attorney, Agent, or FirmSughrue, Rothwell, Mion,

Z inn & Macpeak [5 7] ABSTRACT I Oblique holes are drilled into a formation from a well bore hole, packed with explosive charges, and simultaneously detonated. The holes are drilled at the same level and angle with respect to the bore hole, and are evenly spaced around its periphery. An implementing apparatus includes a tool carrier that is lowered into the bore hole and anchored in place, a flexible shaft drilling tool that is lowered into the carrier, and a packing tool for placing the charges,

7 Claims, 8 Drawing Figures PATENTEDHAR 1 9 m4 3797'. 576

SHEET 1 OF 3 INVEN MS JEAN PAUL AZALBEET ADE/EN G/fAl/D wz 726K000, M, er "f Arm/elven" 3.797.576 PATENTEUMAR19 I974 SHEET 2 [IF 3 SHEET 3 BF 3 PATENTEUMAR 19 I974 METHOD AND APPARATUS FOR BREAKING UI ROCKS CONTAINING LIQUID OR GASEOUS HYDROCARBONS BY MEANS OF EXPLOSIVES I BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method and apparatus for breaking up rocks that contain liquid or gaseous hydrocarbons, particularly rocks around a production or injection well, so as to increase the productivity or injection index of the well.

2. Description of the Prior Art Presently known breakup methods employ one or more explosive charges which are placed in a production well on the level of the rock to be cracked or a liquid explosive which is forced either directly into the rock or into one or more cracks started by hydraulic or chemical breakup.

In the first case, the inconveniences observed often cancel out the advantages obtained. Ineffect, it is impossible to obtain good contact between the charge and the rock because the charge must be capable of being lowered to the bottom of the well. In other words, it must have a cross section smaller than that of the bore hole. Experience has shown that the rock is broken up very locally and that the network of cracks does not spread much. Moreover, because of the distribution of the confinement stresses around a well, the explosion starts radial cracks which do not isolate finished volumes of rock. Because of this, the cracks opened in the course of the explosion close up again and there is thus no appreciable gain in terms of permeability and hydrocarbon output. The damage inflicted on the installations at the bottom, on the other hand, is quite considerable: deterioration of the tubing, casing, cementing,

. 2 experience shows that, regardless of the damage to the well installations, the explosion produces the compacting of the limestone and therefore clogs the formation.

, Tests performedin gritty sandstone matrixes do not etc., in addition to which we have the accumulation, in

the well, of rock fragments broken up by the explosion and these often are harmful to the production of the subjacent levels.

In the second case, the situation involves the injection of a liquid explosive into natural cracks or cracks started by hydraulic breakup and possibly enlarged by the action of an acid. Regardless of the difficulty of emplacing a liquid explosive in a rockwhose temperature is more than 60 C, because of the risk of spontaneous detonation of a conventional liquid explosive, experience shows that, if the formation to be treated is a per meable rock, the injected explosive generally is not able to detonate because of its dispersed state in the rock and the mixtures which are formed during the injection between the explosive and the hydrocarbons. Only very porous sand formations, in other words, formations which are highly permeable, can transmit the detonation. In this case, however, the rather poorly consolidated character of the formation'is accompanied by the total break-up of the rock which is thus invaded by the explosive and this breakup causes the well to become clogged.

If the rock has a low permeability, the injection of the liquid explosive is accomplished by using various methods. If, for example, we are dealing with a limestone formation impregnated with oil or gas, and to the extent that this formation involves natural fissures, it is possible to enlarge these fissures by injecting 15% hydrochloric acid. If this formation does not involve any fissures, one can start them by hydraulic breakup. But

yield any definitely better results.

In the two cases visualized there, it is necessary to use a drilling apparatus in order to return a portion of the equipment, such as tubing, etc., back to the surface, to cement the bottom of the hole, to putsand above the charge or to exert any pressure on the liquid charge and to restorethe hole after the explosion. These, therefore, are very cumbersome operations whose advantages are considerably less than those visualized here.

SUMMARY OF THE INVENTION One purpose of this invention is to provide a method for breaking up the ground around petroleum wells according to which, on the level of the zone tobe broken up and from the well itself, we make at least one oblique drill hole with respect to the axis of the well and this drill hole has a diameter smaller than the radius of the well. The axes of the well and of the oblique drill hole are essentially in the same plane. We then place a charge at the bottom of said oblique drill hole, pack the charge, and detonate it.

Contrary to known methods of breaking up rocks by explosives, recommended to increase the productivity index, the charge is no longer placed in the well but instead is put into the formation at a certain distance from the well. One of the first consequences is to avoid damage to the well because the explosive charge is placed at a certain distance from the axis of the well, even though this distance may be rather small, such as, for example, one meter. In this way we can prevent damage due to charges having the same power but placed in the well itself.

Moreover, for similar charges, the fractures obtained no longer have a tendency to disappear and the limestone ground no longer undergoes the compacting effeet which works against the permeability of the ground and which consequently hinders the flow from the well.

It is difficult to give a full explanation of the results which are obtained by using the method involved in this invention. The excellent breakup of the rock accomplished under these conditions is partly due to the reflection of the explosive shock wave upon the uncut walls of the well drill hole. Furthermore, we know that the horizontal stress 02, the radial stress at and tangential stresses have the following values at a p i tth2 w. m

when 0 (v/l V)o' where (r, is the vertical stress, V is the Poisson coefficient, a is the radius of the well, and r is the distance from the point to the center of the well.

In conventional methods, where radial fissures start from the well, this dissymmetry tends to close these cracks. On the other hand, any possible concentric fissures, whose effect on the output is zero, have less of a tendency to close up again.

In the case of the method involved in this invention, the radial fissures start from a lateral oblique drill hole in a zone where the difference between a, and (r, is less and we find that, regardless of their orientation, these fissures have less of a tendency to close up again and are productive.

Moreover, the use of the energy released by the explosion is more complete because, in the proximity of the charge placed in the oblique drill hole, we have a surface that reflects the stress waves emitted during the explosion.

Thus we see that the radial compression wave is reflected into a radial traction wave creating a network of fissures roughly concentric with respect tothe oblique drill hole, outlining-with the first radial fissures and the concentric fissures formed by the train of incident waves-a network of cracks delimiting finished volumes, thus preventing the disappearance of the radial fissures.

After the breakup of the rocks, an increase in permeability is observed which is greaterthan in the previously used methods and the well is not damaged in any way.

Another object of this invention is to provide a method of the type described, where the distance from the bottom of the oblique drill hole to the axis of the well is between 0.50 m and 2 meters and where at least two identical oblique drill holes are made distributed around the well in a symmetrical fashion, with the explosion of these identical charges taking place simultaneously.

The effect of the simultaneousness of the discharge further strengthens the effects obtained with a single oblique drill hole so that the cracks are distributed uniformly around the well, without any of the inconvenience encountered when the explosion is performed from the well itself, with or without the injection of liquid explosives into the cracks.

This method is further improved as a result of the better cooperation or tie-in ensured by the separate charges introduced into the oblique drill holes, whose cross section is furthermore much smaller than that of the well. It is thus possible to detonate a minimum mass of explosives because of the good tie-in between the rock and the explosive, at such a distance from the well that the cracks can reach the well without damaging the installations. The simultaneous detonations of charges, which crack a pattern around the well, leave the immediate surroundings relatively intact, in spite of the extension of the fissures.

The well can thus bereturned to production or injection immediately after the detonation.

Another purpose of the invention is to provide an apparatus for implementing a method of this type including a tool that involves an anchoring means for holding on in the well that the level at which we want to make the oblique drill hole, a body involving an internal passage with a circular transversal cross section, passing out, on the periphery of the tool, through a cylindrical portion whose axis forms a given angle with the axis of the well, a flexible shaft inside said passage, as well as moving means that cooperate with one end of said flexible shaft in order to rotate, advance, or withdraw it, the other end of said shaft being equipped with a drill carrier and a drill.

It thus suffices to insert said tool 'into the well down to the desired level, to manipulate its anchoring device and then its means for the movement, advancement, and rotation of the flexible shaft in order to start an oblique drill hole which continues automatically in the direction started by the inclined cylindrical passage of the body of the tool.

Another object of the invention is to provide'an apparatus of this type in which said tool is made up of two separable parts. One is called the tool carrier and in volves a tubular envelope with a circular section carrying said anchoring means, openings equally spaced over a straight section of the envelope, and an orientation device. The other part is the tool itself, including, in addition to the passage with the circular cross section and its flexible shaft, a lower portion that cooperates with said orientation device, so that the simple descent of said tool into its tool carrier brings about the coincidence of the opening of said passage with one of the openings of said tool carrier, while the raising of the tool with respect to the tool carrier brings about the rotation of the tool in order to move the opening of the cylindrical passage opposite the following opening of the tool carrier.

One can thus perform successive drilling operations without having to bring the tool back to the surface because the tool carrier orientation device guarantees the correct orientation of the oblique drill holes made around the well.

Another object of the invention is to provide a method using an apparatus of this type, according to which we return said tool to the surface, after the completion of the oblique drill holes, however without its tool carrier, and according to which we lower a second tool including: (a) a body with as many passages opening up obliquely at the periphery of the tool as we have openings in the tool carrier, each of these passages involving a flexible tube containing an explosive charge, its detonator, and a packing means; (b) a lower portion for cooperating with the orientation device of said tool; (0) a first means for moving and simultaneously introducing all flexible tubes into the previously made drill holes; and (d) a second means for simultaneously injecting a fluid into each one of the'flexible tubes and pushing back the explosive charges, their detonators, and their packing means outside the tube, said first means returning said tubes into the interior of their housing.

In a single operation, consisting of lowering the second tool after withdrawing the first tool, we can thus correctly and automatically arrange all of the charges which we' can then set off, after bringing the second tool and its tool carrier back up, either by manual control using an electrical connection, or by automatic control using delayed-action detonators.

In this way we can make precise oblique drill holes, we can simultaneously place charges and we can detonate them by simple, rather inexpensive and very safe means in a very short time; the method recommended here furthermore makes it possible almost immediately to resume the exploitation of the well.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a schematic plan view representation of the type of crack development obtained by the explosion of a charge in a well;

FIG. 2 is a schematic representation of the cracks in an axial cross section of a well where the explosion takes place;

FIG. 3 is a schematic plan view representation of the type of crack development obtained by the application of the method involved in the invention;

FIG. 4 is a schematic representation of the cracks obtained by the application of the method involved in the invention, in an axial cross section through the well;

FIG. 5 is a section containing the axis of the oblique well drill hole;

FIG. 6 is a schematic view of a longitudinal cross section of a tool used in making the oblique drillings;

FIG. 7 is a schematic view of a longitudinal cross section of a tool for the automatic placement of the explo sive charges; and

FIG. 8 is a schematic representation of a dynamite cartridge, carried by the tool in FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENT In order to make the explanation of the method for breaking up ground around petroleum wells clearer and in order to be able easily to compare the results obtained from the use of the invention and from earlier methods, we have shown, in FIGS. 1 and 2, the cracks obtained in the case of an explosion of a charge placed in a well on the level of the zone to be broken up and in FIGS. 3 and 4 we have shown the cracks obtained from the use of the method involved in this invention.

In FIGS. 1 and 2, the walls of the well are shown at 1. Lines 2 correspond to the dislocation zone produced by the explosion set off in well 1. Lines 3 are the radial fractures and lines 4 are concentric fractures which may exist because of the reflection of the radial waves upon a free surface or upon a medium whose sound propagation speed is different. We can add to these fractureswhich depend only on the environment in which the well was drilled-certain smaller cracks, such as those at 5, which are due to the reflection of a plane wave being propagated vertically. Experience has shown that, in fact, cracks 3,.which are the biggest, have a tendency to close up again, so that the explosion of the charges in the well itself does not bring about an increase in the circulation of the injected fluid or of oil collected.

In the case of FIGS. 3 and 4, we explode the charge in the oblique drill hole whose walls are shown at 6. We find a dislocation zone 7 around the immediate vicinity of the place of the explosion but this zone is outside well 1. Radial cracks 8 are displaced and this time start from drill hole 6, spreading in all directions, so that some of them come out in the proximity of walls 1 or the well. The concentric cracks appear at 9 due to the action of the train of waves reflected from the walls 1 of the well. This time they can be anticipated and they are bigger than in the case of FIGS. 1 and 2. These crack developments are due to the radial stress wave which is reflected intoa traction wave and they have a tendency to dislocate the radial cracks 8 and to prevent them from closing, while cracks 10, due to the influence of the train of reflected waves being propagated along the oblique drill hole, result in the outlining of well-delimited earth volumes whose structure prevents the closing of the crack development network. Experience has shown that the use of oblique drill-holes having a diameter between 2 and 6 cm, and more generally comprised between one-sixth and one-third of the diameter of the well, permits the fissures zone to be accurately located and prevents any damage to the wall of the well when the oblique drill-holes are symmetrically disposed around the well.

This particular structure is found again around each of the lateral drill holes 11, in FIG. 5 arranged symmetrically with respect to the well.

In the example selected here, the planes of the four drill holes 11 are arranged at with respect to each other and the charges 12 are arranged at the bottom of the drill holes and at the same level.

The simultaneous firing of the charges has the effect of adding up the stresses coming from each explosion and creating a crack development in places which would normally remain intact.

Methods for lowering and raising the tools are known in themselves and we will therefore confine ourselves to a description of the two tools cooperating with one and the same tool carrier and ensuring the implementation of the breakup method which we have just described.

The tool carrier includes a tube 13 shown in FIG. 6, which contains the body 17 that includes all of the components of the drilling tool as such. It is lowered with an electrical multiconductor cable 14, connected to the circuits of the tool, by connector 15. The tube 13 of the tool carrier has been perforated with a certain number of holes 16, equal to the number of lateral oblique drill holes which we want to make: in other words, four in the example selected here. Guides 18, as well as anchoring blocks 19 are provided on tube 13.

The anchoring blocks, which can be of any known type, fix the position of tube 13 with respect to the ground and are coupled with piece 20. The latter makes it possible to fix the orientation of the body 17 of the tool with respect to the tube 13. A simple device, schematically indicated by piece 21, automatically orients the body 17 with respect to the piece 20 so that it can present an opening similar to the holes 16 of tube 13 opposite one of these holes. This device can involve two or four studs cooperating with four vertical grooves and four oblique grooves, so that the first vertical and upward sliding action of the body 17 of the tool, with respect to the tube 13, anchored in the well at the selected level, moves each of the studs through the oblique grooves toward the following vertical groove, while the lowering of the body 17 once again brings about the coincidence of a similar opening of body 17 and another hole 16 of tube 13.

The power required for the drilling tool is furnished by electric motor 22 which rotates in two directions. It drives shaft 23 which is grooved on the outside and whose length is equal to or greater than the length of the hole to be drilled.

Around this shaft there slides a shaft 24 which is grooved on the inside and which carries a piston 25 which has the same axis. This piston slides inside a hydraulic jack 26, activated by a hydraulic circuit fed by pump 27, driven by motor 22. The piston 25 thus makes it possible to apply a descending or ascending force to the grooved shaft 24.

Flexible shaft 28 is attached to the lower portion of shaft 24. This shaft at the same time transmits the rotation movement which is imparted to it by shaft 24 dur ing the rotation of shaft 23 and the translation movement ensured by jack 26.

A rigid straight casing 29a, which prolongs a rigid, curved casing 29b, serves as a slide for the flexible shaft 28. The rigid portion 290 has a length equal to that of the hole to be drilled laterally. Due to the effect of the curvature of portion 29b of the rigid casing, shaft 28 hits wall I of the well at an angle determined by the direction of the last straight portion of the passage 29b.

The drill carrier 30, equipped with its drill 3E, thus enables us to make an oblique drill hole. The drill is selected from among types of tools which throw the debris toward the outside, without leaving any core samples in the center of the drill hole.

The drill 31 advances under control of jack 26 which is supplied by pump 27. The control circuit includes a chamber 32 which balances the internal pressure with respect to the ambient pressure and an electrically controlled distributor 33 which makes it possible to raise or lower the piston or to keep it in a certain position.

The drill is lubricated by the cooling and lubrication pump 34 which is possibly mounted on a second shaft of the motor 22. The pump 34 sucks in the surrounding fluid through housing 35 and forces it back around motor 22 which it cools. The fluid is collected on the level of the upper portion ofthe rigid guide 2a and penetrates between the shaft 24 and the guide 290.

At the junction, between shaft 24 and shaft 28, we

. cause the penetration ofa portion of the fluid inside the shaft 28 so as to channel this fluid toward the drill 31 into which it comes out. In this way, friction between shaft 28 and its guide 29a-29b is reduced.

The drilling debris, moved along the cooling fluid, falls into basket 36.

A retractable finger or pawl 51, traversing the bottom of cylinder 26, is used to stop the piston 25 at a predetermined level thus to limit the advance of the drill 31. This finger has, in its upper portion, a screw threading which engages a conventional movement mechanism shown schematically at 52.

When piston 25 butts into pawl 511, presumed to be in its outside upper position, the overpressure, produced above the piston, causes the safety valve 53 to open. This valve now provides communication between the portion of the cylinder where the overpressure develops and the conduit 54 which is used to force the fluid of the jack back during the descent of the piston.

The mechanism 52 can be manually controlled at the surface or it can be placed in action automatically, depending upon the nature of the work to be done.

The four drill holes are made without the development of any core samples with the help of a tool, which has just been described, in an extremely simple fashion. In effect, after the placement of tube I3 by conventional methods, it suffices to lower the tool 117 with its electrical cable 14 so that the tool will automatically engage in tube 13 in a position causing its lateral opening to coincide with one of the holes 116 by virtue of the orientation device 21. The pawl 51 is in the low position, the motor 22 is started up from the surface and the drill attacks the rock wall. At the end of the run, the intensity absorbed by the motor decreases. We now change the direction of rotation from the surface.

The flexible shaft 28 and its drill then enter guide 29a-29h of the body of the tool which we partly raise up again with the cable and which we then lower again. In this movement, the orientation device causes the tool to pivot by 90 in the example chosen. It suffices to start the drill over again in order to make the second lateral drill hole and to keep going in this way until we come to the last drill hole.

When we want to produce core samples, the pawl 51 is moved upward for a length equal to the core sample which we want to collect. In the first run, the drilling operation may be performed as we have just described. However, when the pawl 51 is in the top position, the drilling operation, without production of core samples, is stopped the moment piston 25 runs against pawl 51. We then raise the tool 17 again, while the tube 13 remains in position, and we replace the drill 31 with a core sampling tool. We remove the pawl SI and we once again lower the tool 117 by means of the electrical cable. The start of rotation of the electrical motor 22 enables us to lower the piston down to the bottom of cylinder 26 and consequently to remove a core sample from the place where we want it, that is to say, in the case considered here, at the place where we want to put an explosive charge. We than move the core sample into the interior of casing 29b and we raisethe tool again.

After this operation, we lower the tool 37 by means of the electrical cable without touching the tool carrier which is still anchored in the well. Tool 37, shown in FIG. 7, is used to place the explosives and to detonate them.

This apparatus involves an electric motor 38 which rotates in two directions and which can tolerate the temperature and pressure conditions at the bottom. This motor includes a reduction unit which moves a threaded shaft 39. A shaft 40, threaded on the inside, is screwed on shaft 39 and, in its lower portion, carries a piston 41 which slides in cylinder 42.

In the top position, the piston 41 is attached to the cylinder 42 by means of pins 43, which shear under a certain effort.

The bottom of the cylinder involves passages whic are closed off by valves 4-4, which are calibrated for a certain pressure, and which communicate with as many rigid hollow rods 45 as there are holes to be stuffed. These rigid hollow rods are shorter than the drilled lateral holes. They are attached, in their lower portions, to flexible casings 46 which are made of metal or plastic material and which have the same length and which slide in rigid guide tubes 47 whose openings are opposite the openings 16 of the tube carrier 13. Each casing 46 ends in the rigid cylindrical piece 48 in which an assembly is contained including the detonator and the delayed-action device. Piece 48 can also include the explosive charges or it can be replaced by a simple prolongation of tube 46 containing a rigid envelope housing a complete explosive assembly.

An electrical contact system stops the motor 38 when the piston 41 runs against the lower face of cylinder 42. This system is shown schematically at 49.

The solid, pelletized, or granulated explosive is contained in cylindrical plastic pouches which we insert in the flexible casing 46. The detonators and possibly the delayed-action devices are attached at the end of the casings, while rods 45 and the space remaining in the casings 46 can be stuffed with glass balls.

The cylinder 42 is filled with an inert liquid 50.

The apparatus thus charged is lowered into the well and is automatically placed in position with the help of the orientation device 2R of the tool carrier.

The motor 38 is started up and thus lowers the shaft 40, consequently bringing about the simultaneous penetration of the flexible casings 46 into the lateral drill holes. When the cylinder has been lowered by a predetermined length which is less than that of the hole, its movement is arrested by a stop. The pins 43 of piston 41 are sheared off and the piston, during its descent, ejects the liquid 50 through calibrated flap-valves 44. The liquid thus ejected'at a pressure greater than ambient pressure forces the charges and the detonators to come out of casings 46. When all of the liquid 50 has been forced back outside the cylinder, an end-run contact stops the motor. One can then start it moving again from the surface in the opposite direction in order to cause the casings 46 to return into the body of the tool which we raise with the tube 13.

It goes without saying that the liquid 50 can be replaced with a liquid explosive.

The detonation can be controlled from the surface. In this case, the detonators are attached to a solid and thin electrical cable. The detonators are provided with grips which anchor them in the hole. The electrical cables contained in the tool are unwound during the simultaneous raising movement of tool 37 and tube 13. Firing is controlled from the surface by a contact which is activated when the tool has beenraised back up suffi- I ciently.

We can also use an automatic trigger. In this case, the detonator is connected to an electrical delay system which is placed in the same envelope and which is triggered during ejection from casing 46. The delay time may be as much as several hours and we thus have all the time we need to get the tool and the tool carrier out of the well.

In order to make the placement of the explosive safer, we introduce, into the metal portion 48, a dynamite cartridge involving a retarder 55, FIG. 8, which is held in tube 48 either by shear pins or, very simply, by gentle friction inside the tube. A lock illustrated schematically at 56 prevents the premature emergence of the retarder outside its. housing &8 and thus prevents the operation of the triggering contact 57. When the cartridge is charged, the operator can thus manipulate the charges in complete safety. Detonator 58 is housed, in the usual manner, in retarder 55 by means of simple screwing, for example, and the liquid or solid charge, indicated schematically at 59, surrounds the detonator. The rest of the tube can be sealed with glass balls 60 which guarantee the packing of the charge.

Although we have described here only one way of making the tool used in the invention when we want to increase the speed of operations, it is clear that the invention is not exclusively confined to the breakup method described here by necessarily making four lateral drill holes. The drill holes may be any number and that number depends primarily on the topography of the subsoil. Likewise, these drill holes, with or without core samples, can be made by the simple deviation of a conventional drill tool. As for the tool used in placing the charges, it is clear that the apparatus can involve a single charge carrying tube or any number of such tubes. These tubes can have a length equal to that of the drill holes that have been made, and the charges are always arranged at the end of these tubes. in this case, the breakage of the pins 43 makes it possible to separate the cylinder 42 physically from piston 41 and we can continue the descent of the piston 4-1 while progressively bringing back up the tubes 46, until the cartridge has been completely disengaged. This return upward can be assured, for example, by a simple spring which has been compressed by the movement of the bottom of the cylinder 42 prior to the breakage of the pins 43.

We claim:

1. In a method for breaking up the earth formations surrounding a petroleum well by 1. drilling subsidiary holes radiating from the petroleum well,

2. placing explosive charges in the and g 3. detonating the charges, the improvement wherein the subsidiary holes are drilled by: a. anchoring a tool carrier having an orientation device at the depth of the formation to be broken, b. lowering within said tool carrier a tool including a rigid body with a passage for guiding a flexible shaft carrying a drilling means, said passage coming out at an opening in the tool carrier and having the same axis as the-hole to be drilled, c. returning the flexible shaft into its guide device after drilling a first hole, changing the orientation of the tool, e. drilling a second and or moreadditional holes in the same manner, f. returning said tool to the surface,

lowering a second tool equipped with an orientation device into the tool carrier, said second tool carrying as many flexible tubes and guide bodies as there are subsidiary drill holes, each of the tubes containing an explosive charge, a detonator, and a packing means, h. pushing said flexible tubes to the inside of said subsidiary drill holes, i. ejecting said charges, detonator, and packing means into the drill holes, j. removing the tool carrier and its tool back to the surface, and k. detonating the charges simultaneously.

2. A method as defined in claim 1 wherein the distance from the bottom of the subsidiary drill hole to the axis of the well is between 50 and 300 cm, and the diameter of the hole is from one-sixth to one-third the diameter of the well.

3. A method as defined in claim 1 wherein a. at least two subsidiary holes are drilled,

b. said holes are identical and are distributed symmetrically around the axis of the well, and

c. an identical explosive charge is placed at the bottom of each hole.

4. A method as defined in claim 1 wherein the angle of the axis of the subsidiary hole with respect to the axis of the well is between 20 and 5. A method as defined in claim 1 wherein core samples are taken from the holes after they are drilled and before they are loaded with the explosive charges.

6. A method as defined in claim 5 wherein the core sampling is implemented by attaching a core sampler at the end of the flexible shaft and by rotating and advancing the flexible shaft.

7. A method as defined in claim 1 wherein the pushing of said flexible tubes is arrested before their ends have reached the bottoms of the drill holes, and the charges, detonator, and packing means in the tubes are simultaneously ejected into the holes.

subsidiary holes,

UNl'il'll) S'IA'llm'i PATENT ()FFIII". Cllli'llFHIATII ()F C(HilillI'HUN Patent No. 3,797,,576 Dated March 19,1974

lnventofls) Panl Azalbert et a1 is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In The Specification:

Column 2, line after "visualized" delete "there" and insert here line5Z delete "[2" and insert [z delete "6 2 =(v/1 V) [1" and insert (2 line 56 v/(lv) (1 after "Well" delete "that" and insert on Column 3, line 53 Column 5, line 44 after "or of" insert the line 52 after "walls 1" delete "or" and insert of Golumn 6, line 52 after "drives" insert a Signed and sealed this 29th day of October 1974.

(SEAL) Attest:

McCOY GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents 5 po'mso (w'sg) USCOMM-DC flO376-P69 U.S GOVERNMENT PRlNTlNb OFF CE: I969 0-366-33 

1. In a method for breakIng up the earth formations surrounding a petroleum well by
 1. drilling subsidiary holes radiating from the petroleum well,
 2. placing explosive charges in the subsidiary holes, and
 3. detonating the charges, the improvement wherein the subsidiary holes are drilled by: a. anchoring a tool carrier having an orientation device at the depth of the formation to be broken, b. lowering within said tool carrier a tool including a rigid body with a passage for guiding a flexible shaft carrying a drilling means, said passage coming out at an opening in the tool carrier and having the same axis as the hole to be drilled, c. returning the flexible shaft into its guide device after drilling a first hole, d. changing the orientation of the tool, e. drilling a second and or more additional holes in the same manner, f. returning said tool to the surface, g. lowering a second tool equipped with an orientation device into the tool carrier, said second tool carrying as many flexible tubes and guide bodies as there are subsidiary drill holes, each of the tubes containing an explosive charge, a detonator, and a packing means, h. pushing said flexible tubes to the inside of said subsidiary drill holes, i. ejecting said charges, detonator, and packing means into the drill holes, j. removing the tool carrier and its tool back to the surface, and k. detonating the charges simultaneously.
 2. A method as defined in claim 1 wherein the distance from the bottom of the subsidiary drill hole to the axis of the well is between 50 and 300 cm, and the diameter of the hole is from one-sixth to one-third the diameter of the well.
 2. placing explosive charges in the subsidiary holes, and
 3. A method as defined in claim 1 wherein a. at least two subsidiary holes are drilled, b. said holes are identical and are distributed symmetrically around the axis of the well, and c. an identical explosive charge is placed at the bottom of each hole.
 3. detonating the charges, the improvement wherein the subsidiary holes are drilled by: a. anchoring a tool carrier having an orientation device at the depth of the formation to be broken, b. lowering within said tool carrier a tool including a rigid body with a passage for guiding a flexible shaft carrying a drilling means, said passage coming out at an opening in the tool carrier and having the same axis as the hole to be drilled, c. returning the flexible shaft into its guide device after drilling a first hole, d. changing the orientation of the tool, e. drilling a second and or more additional holes in the same manner, f. returning said tool to the surface, g. lowering a second tool equipped with an orientation device into the tool carrier, said second tool carrying as many flexible tubes and guide bodies as there are subsidiary drill holes, each of the tubes containing an explosive charge, a detonator, and a packing means, h. pushing said flexible tubes to the inside of said subsidiary drill holes, i. ejecting said charges, detonator, and packing means into the drill holes, j. removing the tool carrier and its tool back to the surface, and k. detonating the charges simultaneously.
 4. A method as defined in claim 1 wherein the angle of the axis of the subsidiary hole with respect to the axis of the well is between 20* and 70*.
 5. A method as defined in claim 1 wherein core samples are taken from the holes after they are drilled and before they are loaded with the explosive charges.
 6. A method as defined in claim 5 wherein the core sampling is implemented by attaching a core sampler at the end of the flexible shaft and by rotating and advancing the flexible shaft.
 7. A method as defined in claim 1 wherein the pushing of said flexible tubes is arrested before their ends have reached the bottoms of the drill holes, and the charges, detonator, and packing means in the tubes are simultaneously ejected into the holes. 